Measurement techniques commonly used for calculating packet delay through a network disrupt the flow of data and are only able to provide timing resolutions down to +/−10 millisecond. This is adequate for most network throughput applications. However, accuracy in the sub-millisecond range (resolutions down to 100 microseconds) is necessary to quantify the impact of network degradations on applications that are highly sensitive to network delay and jitter, such as Voice over Internet Protocol (VoIP) and Video on Demand (VoD) applications.
Measuring the delay between two points in a network with high (sub-millisecond) resolution is challenging because networks often include many segments with variable delay. In addition to the transport delay of each segment determined by the actual wire length of the connection, the router or switch at each end of each segment introduces additional delay caused by packet processing and queuing delays that are highly non-deterministic. The processing and queuing delays are dependent upon the type and configuration of the routers and switches, as well as the existing user traffic routed through the routers and switches in a myriad of directions. The multiplicity of segments that generally make up a large network increase the complexity of deterministically calculating the delay over a data network.
Conventional network delay measurement techniques generate special network traffic to accomplish the delay measurement of a data network, but these techniques are inadequate in measuring the network latencies of existing network traffic at high resolutions. First, the intrusive traffic generated by these techniques is often an unrepresentative approximation of user traffic and therefore is inaccurate and unreliable. Generated traffic cannot be guaranteed to follow the same path with the same priority and through the same queues as existing user traffic. Also, the traffic introduced by conventional network delay measurement techniques degrades the quality of service between users over the network and can have an impact on the accuracy of the delay measurement. The special network traffic injected for the latency measurement is itself additional traffic on the network that is unavoidably accounted for in the latency calculation. Finally, since these techniques can only report the delay measurement at the exact instant that the intrusive traffic is generated, any increase in the rate of latency measurements will further disrupt the flow of existing network traffic and degrade the quality of service of the network to users. Thus, a need exists for a method and apparatus for calculating network traffic within a data network.